1. The Field of the Invention
This invention relates to a heat-storing apparatus, which comprises a heat-storing material of latent heat type placed in a heat-storing vessel, where heat is stored or released by a phase change of the heat-storing material of latent heat type, and more particularly to a heat-storing apparatus, which stores solar heat, waste heat, heat generated by use of midnight electric power, etc. and releases the stored heat, when required.
2. The Prior Art
The conventional heat-storing apparatus uses a heat storing material of sensible heat type such as water, stone fragments, etc. as a heat-storing material, but such heat-storing material has a low heat-storing capacity, so that the heat-storing apparatus must have a considerably large size. Thus, attempts have been recently made to make the heat-storing apparatus smaller in size but larger in capacity by using a heat-storing material of latent heat type which utilizes the latent heat appearing at solidification and melting of inorganic hydrated salts such as sodium thiosulfate pentahydrate and calcium chloride hexahydrate. Various inorganic hydrated salts are available for desired temperature ranges, and for a temperature range of 40.degree. to 50.degree. C. , sodium thiosulfate pentahydrate (Na.sub.2 S.sub.2 O.sub.3. 5H.sub.2 O) is a promising heat-storing material because it has a melting point of 48.degree. C., a solidification point of 45.degree. C. and a high latent heat such as 82 cal/cm/.sup.3, and is also cheap. However, when the inorganic hydrated salts are subjected to repetitions of solidification and melting, a phenomenon of separating the salt into a salt having a high melting point and a salt having a low melting point (phase separation phenomenon) takes place due to the nature of the salt, that is, the melting point corresponding to a peritectic point, and consequently the salt will not release the latent heat at the desired temperature (melting point) in the end.
Sometimes, the salt undergoes supercooling and fails to undergo solidification at a temperature by 20.degree. to 30.degree. C. lower than the melting point and thus the stored heat is not released at the desired temperature (supercooling phenomenon).